The present invention relates to an infinitely adjustable cone disc transmission and the production of axial pressure forces of the cone discs on pulling means rotating between these cone discs via hydraulic tensioning means, which are arranged on the transmission shafts and axially influence each of the cone discs which are displaceably arranged on the respective transmission shaft. The tensioning means and the pressure medium conduits contacting the same are charged with a pressure medium which is supplied by a pump. A torque sensor is provided in the reflux of the control valve on the drive shaft of the transmission. This torque sensor throttles, as a function of the load, the reflux of the pressure medium as a result of the movement of two valve members relative to one another as a function of the torque and thus determines the system's base pressure. A revolution sensor is provided on the drive shaft, so as to provide, as a function of the rotational speed, pressure medium to a control element which, in connection with a member for adjusting the drive power, acts upon the transmission ratio by way of the control valve.
This type of cone disc transmission is disclosed in DE 4,039,830. There, a pressurizing valve is additionally connected to the input of a torque sensor in order to throttle the reflux of the pressure medium as a function of the transmission ratio, such that the entire throttling of the pressure medium reflux, and thus the corresponding control of the cone disc transmission, occurs as a function of the power and the transmission ratio. Such a pressurizing valve may also be considered for use in the present invention.
In the case in which such transmissions are known to be used in motor vehicles, the problem of always ensuring the transition of the transmission ratio to the starting position independent of the respective driving conditions at the end or during an interruption of the driving is solved by special means provided there. This is especially the case with respect to emergency braking, because under normal driving conditions the time available and the quantity of pressure medium supplied by the pressure medium pump are sufficient to move the transmission into the start-up transmission gear. The start-up transmission ratio itself is characterized in that the pulling means at the driving-pulley assembly has the smallest travel radius and at the driven-pulley assembly it has the corresponding greatest travel radius.
However, a further problem occurs if the motor cannot be started due to a malfunctioning and the vehicle must be towed. In accordance with the start-up gear ratio, which exists in any case, the driving-pulley assembly is fully spread apart and must be towed along at high speed without the hydraulic tensioning means being supplied with pressure medium, because, if the engine is at rest, the pressure medium pump does not work either. The result may be permanent slipping and damage to the cone disc transmission, particularly if the drag moment at the drive is increased by additional devices, for example, a reversing gear including couplings.